Base station in a cellular radio system and a cellular radio system

ABSTRACT

A base station for a cellular radio system including switching centers and base stations connected thereto by time-division telecommunication links. The base station includes one or more transceiver units for establishing radio links, a multiplexer/demultiplexer for multiplexing transmission channels on the telecommunication links, for extracting synchronization and clock signals, and for demultiplexing data to be sent from the base station to a transmission channel of the telecommunication link. The base station further includes switches for switching respective transceiver units to respective transmission channels of the respective telecommunication links.

BACKGROUND OF THE INVENTION

This application claims benefit of international applicationPCT/FI94/00207 filed May 25, 1994.

Field of the Invention

The invention relates to a base station for a cellular radio systemcomprising switching centres and base stations connected thereto throughtime-division telecommunication links, this base station comprising:transceiver units, a multiplexer/demultiplexer means for multiplexingthe telecommunication links and for demultiplexing data to be sent fromthe base station to the telecommunication link and, a switching meansfor selectively switching the desired transceiver unit to the desiredtelecommunication link.

Background of the Invention

In typical cellular radio systems the switching centres, e.g. mobileservices switching centres, are in contact with mobile phone subscribersthrough radio transmitters of base stations. Base stations can beconnected to switching centres via base station controllers. A basestation of the prior art comprises an antenna unit to which one or moretransceiver units are connected, each of the transceiver units beingconnected via a multiplexer/demultiplexer means to a transmissionchannel of a telecommunication link and further, either directly or viaa base station controller, to the switching centre of the cellular radiosystem.

A prior art solution is described in the publication EP 439 926, whichdiscloses a base station of a radio communication system where thecontrol unit of the base station can switch any radio unit through a busto a digital interface circuit. The object of the cited reference is toprovide a system which enables flexible handling of both analog anddigital radio channel units in the same system. The problem with thesolution according to the cited EP publication is that the base stationdisclosed therein is not capable of recovering from a situation where afault has occurred in one of its transceiver units during normaloperation. The solution disclosed does not possess a feature by means ofwhich the operations and maintenance unit of the system wouldcontinuously receive fault information on the occurrence of faults intransceivers and could, on the basis of this fault information, switchthe faulty transceiver unit off and, correspondingly, switch on a new,undamaged transceiver unit to replace the faulty one.

In the prior art solutions it has been impossible to replace atransceiver unit which transmits a certain transmission channel of atelecommunication link to the radio link and which is possibly faulty orrequires maintenance with another, operative transceiver unit in aflexible manner and by remote control.

SUMMARY OF THE INVENTION

The object of the present invention is to obviate the above problemspertaining to the prior art and to provide a base station which flexiblyboth allocates and releases radio channels, and a cellular radio system.

This new type of base station for a cellular radio system is achievedwith a cellular radio system according to the invention, which ischaracterized in that the switching means for the base station is a timeslot switch comprising: a time slot counter for synchronizing the timeslot switch with the time slots of the time-division bus, a time slotselection register responsive to operations and maintenance informationincluding time slot selection data for time slot-specific storing andreading of the time slot selection data, a comparing means for comparingthe time slot selection data contained in the time slot selectionregister with the state of the time slot counter at a given point oftime in such a manner that the time slot selection data is compared withthe state of the time slot counter and, responsive to the result of thiscomparison, the data contained in the time slot concerned on thetelecommunication link or at the transceiver is transmitted forward, abuffer means responsive to the data supplied by the comparing means forstoring data contained on the telecommunication link and for feeding thedata into a transceiver unit, or for feeding data contained at atransceiver unit into the desired time slot on the telecommunicationlink.

The invention is based on the idea that a transmission channel of atelecommunication link which is to be transmitted to the base station ofa cellular radio system is conducted to a switching means, whichswitches the transmission channel to the desired transceiver unit.

The advantage of such a cellular radio system and base station accordingto the invention is that the desired transmission links, typicallyspeech or telecommunication channels, can be switched to the desiredtransceiver unit operating at the base station on a certain radiofrequency. Typically, this takes place when the radio channel on which acertain speech or telecommunication channel is transmitted is to bechanged or when a transmission channel transmitting and receiving acertain channel is damaged.

Another advantage of the invention is that it is possible to provide thebase station with an extra transceiver unit, which the time slot switchaccording to the invention switches on when necessary. Such a redundanttransceiver unit does not require a separate, fixedly allocatedtransmission channel, but the transmission channel previously used bythe broken transceiver unit will be allocated to it. Thus, it is notnecessary to assign redundant connections to a redundant transceiverunit, which reduces the transmission channel costs of a cellular radiosystem.

It is also to be noted that the invention enables a solution in whichtwo or more base stations have at least partly common transmissionchannels, which can be allocated to the transceiver units of a basestation according to the load of the base station. Therefore, it ispossible to select the number of transmission channels according to howmany transmission channels the base station needs on the average.

Yet another advantage of the invention,is that the operations andmaintenance centre of the cellular radio system, the base stationcontroller or the base station-specific operations and maintenance unitcan, if desired, command a transceiver unit either to operate or to stopoperating automatically, by adjusting a time slot switch connected tothis transceiver unit.

The above-mentioned advantage of the invention leads to a furtheradvantage: as, according to the invention, it is possible to select fromamong the transceiver units of a base station those which are operating,the transceiver units that are not needed can be switched off. Thus, thetransceiver units that have been switched off do not unnecessarilyconsume power at the base station, and they do not disturb the otherbase stations of the cellular radio system or other radio traffic bybroadcasting the identification signal of the base station "in vain".

Still another advantage of the cellular radio system according to theinvention is that it increases the flexibility in the selection of radiochannels used for the transmission of calls to be established from abase station to mobile phones; it is possible to "transfer" more radiochannels to the coverage area of a certain base station from thecoverage areas of other base stations if the base station which is to beexpanded has available "free" transceiver units which can be allocatedfor this purpose and if there are free channels on the radio path.

As compared with the prior art, the invention also has another, verysignificant advantage: when transceiver units of a base station in acellular radio system are to be switched on and/or to be switched totransmit another transmission channel of a telecommunication link to theradio path, this change can be effected by remote control, either fromthe operations and maintenance centre of the cellular radio system orfrom the base station controller. In the prior art solutions the changeof transceiver units or the switching on of a transceiver unit must beperformed manually by a service person sent to the base station, byinterchanging cables connected to the transceiver units of the basestation.

The invention allows, thus, a faulty transceiver unit of a base stationto be replaced with another transceiver unit without having to have aservice person visit the base station. As such a visit is not necessary,an operative transceiver unit needed at the base station is brought intooperation in the case of a faulty transceiver much faster than if itwere necessary to send a service person to the base station. As a resultof this, it is more likely that in the present system that the basestation has a sufficient number of operative transceiver units than itis in the prior art solutions. The overall reliability of the cellularradio system and its base station improves, and thus the service levelof the whole system rises.

A still further advantage of the invention is that the base stationaccording to the invention may be provided with a redundant transceiverunit which, under the control of the operations and maintenance centre,can flexibly be brought into use when the previously used transceiver isdamaged. The recovery of a transceiver from the occurrence of a fault isthus an essential feature of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail andwith reference to the accompanying drawings, in which:

FIG. 1 is a general block diagram of the cellular radio system accordingto the invention and its base station,

FIG. 2 is a detailed block diagram of the time slot switch provided atthe base station of the cellular radio system according to theinvention,

FIG. 3 is a flowchart of the external operation of the time slot switchaccording to the invention,

FIG. 4 is a flowchart of the internal operation of the time slot switchaccording to the invention, and

FIG. 5 is a timing diagram of the internal data transmission busprovided at the base station of the cellular radio system according tothe invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 is a general block diagram of the cellular radio system and thebase station BTS 100 according to the invention. The mobile servicesswitching centre MSC 101 of the cellular radio system may be connectedto a base station controller BSC, which is further connected to the basestation BTS 100 through an Abis interface 103. The Abis interface isdescribed more closely in ETSI/GSM standards GSM 08.51, 08.52, 08.54,08.56, 08.58 and 08.59 from 1992. The Abis interface 103 is connected toa multiplexer/demultiplexer means MUX/DEMUX 104, which transfersinformation carried on the Abis interface transparently as such to theinternal bus of the base station 100; the internal bus is illustrated ingreater detail in FIGS. 2 and 5. The information carried on the Abisinterface can be branched so as to be also transmitted to other basestations by means of the multiplexer/demultiplexer means MUX/DEMUX 104and a junction line 112. From the internal bus of the base station theinformation is conducted to one of the time slot switches 105 accordingto the invention, the structure of which is shown in FIG. 2, and theoperation of which is shown in FIGS. 3 and 4. The time slot switchguides information from the Abis interface, i.e. information on acertain speech or telecommunication channel, to the desired transceiver107, 108, 109. By means of the time slot switch 105 of the invention itis also possible to branch information sent to a certain base station100 so that it is also sent to another base station by selectingtransceiver units 107, 108, 109 of several base stations for theoperation. These transceiver units are selected according to the needthe telecommunication links have for transmission channels. Theselection of transceivers 107, 108, 109 located at several base stations100 by means of the time slot switches 105 of the base stations 100 iscontrolled by the operations and maintenance centre 106 of the cellularradio system. The operations and maintenance centre 106 may beassociated with the base station 100, the base station controller 102,or the switching centre 101 in such a manner that the transmissioncapacity of telecommunication links is allocated to the traffic betweenthose base stations and base station controllers or those switchingcentres of the cellular radio system and base stations that need it. Thetransceivers are known to those skilled in the art and have beengenerally used at base stations of cellular radio systems. Eachtransceiver is connected to an antenna unit 110 which is common to allof the transceiver units and from which the radio messages to be sentare transmitted to the radio path.

FIG. 2 is a detailed block diagram of a representative one, 200, of thetime slot switches 105 provided at the base station of the cellularradio system. The multiplexer/demultiplexer means 104 multiplexes 203data to the internal data transmission bus 202 of the base station 100and demultiplexes 203 in the opposite direction from the bus, i.e. tothe Abis interface 103 between the base station and the base stationcontroller 102. The time slot switch has two directions of operation:downlink, i.e. from the cellular radio system and its switching centretowards a radio subscriber, and uplink, i.e. from a radio subscribertowards the cellular radio system and its network.

The time slot switch and its operation in the downlink direction will bedealt with in the following. A clock signal CLOCK and a synchronizationsignal SYNC are supplied from the multiplexer/demultiplexer means 104 toa time slot counter 204. The time slot counter synchronizes the timeslot switch with PCM data from the Abis interface. The time slot counteris a 5-bit counter which counts time slots from zero to 31(00000→11111). Time slot/setting data of five bits is supplied from alocal operations and maintenance centre LOCAL O&M or a base stationcontroller BSC 106 to a time slot selection register 205. In this casethese five bits constitute the time slot selection data which is storedtime slot-specifically in the memory of the time slot selection register205. The memory of the time slot selection register 205 comprises afive-bit register per each time slot of a transceiver. The registerstores time slot selection data, i.e. the identifier of the time slotfrom which the data to be transmitted to the time slot of thetransceiver should be taken and transmitted forward. If the systememploys 16-kbit/s signalling, the register must use extra bits toindicate in which quarter of a time slot signalling is needed. In thedownlink direction, the time slot counter 204 monitors which timeslot/time slots from the Abis interface 103 is/are transmitted throughthe multiplexer 104 to the internal bus 202 of the base station. Whenthe time slot/time slots set in the time slot selection register 205 bythe operations and maintenance unit is/are received, it/they areobserved by a comparing means 206 connected to the time slot counter andthe time slot selection register. In the comparing means, the valuestored in the time slot selection register 205 is compared with thestate of the time slot counter 204. If the states are identical, e.g.the value 8 has been selected for the time slot in the time slotselection register and the value of the time slot counter is also 8, thedata contained in the time slot concerned is loaded into a buffer means207 connected to the comparing means 206. The information to be sentfrom the buffer means is transferred to a transceiver unit (typicallythere is one transceiver unit per each time slot counter). The entirebase station may comprise several time slot switches 105, (e.g.,200, 201. . . ) and several transceiver units 108, 107. There may, of course, bean optional, even a greater number of transceiver units.

Information to be sent in the uplink direction is supplied from thereceiver of the transceiver 108 to a buffer 217. In the same way as inthe downlink direction, there is in the uplink direction also provided atime slot counter 214, which is synchronized with PCM data from the Abisinterface 103. In its structure and operation the time slot counter ofthe uplink direction corresponds to the counter of the downlinkdirection. The local operations and maintenance unit 106 of the basestation or the operations and maintenance centre of the cellular radiosystem, either in connection with the switching centre 101 or the basestation controller 102, controls a time slot selection register 212. Theidentifier of the time slot into which the signal received by thetransceiver 108 and supplied to the time slot switch 200 concerned is tobe inserted is stored time slot-specifically and through the operationsand maintenance unit in the memory of the time slot selection register212. Per each time slot of the transceiver unit the time slot selectionregister has a five-bit register, which may be expanded in the case of16-kbit/s signalling. In the same way as in the downlink direction, asynchronization signal SYNC and a clock signal CLOCK are supplied 213from the multiplexer/demultiplexer means to a time slot counter 214. Thecontents of both the time slot counter 214 and the time slot selectionregister 212 are conducted to a comparing means 215. The comparing meanscompares the value stored in the time slot selection register 212 withthe value contained in the time slot counter. If these values or statesare identical, e.g. the value 8 has been selected for the time slot inthe time slot selection register and the value of the time slot counteris 8, the data loaded into the buffer 217 is inserted into the time slotassigned for the transceiver unit 108 on the internal time-division bus202 of the base station. From this bus, the data is further transferredby means of the multiplexer/demultiplexer means 104 to the Abisinterface 103 between the base station and the base station controller102. Through the Abis interface the data is transferred to the basestation controller 102 to be further transmitted to the switching centre101 of the cellular radio system.

It should be noted that there must be at least one time slot switch 200,201 per each transceiver unit 107, 108, 109 of the base station. Atime-division 2-Mbit/s bus 202 with separate reception and transmissionlines is used for data transmission between themultiplexer/demultiplexer means and the time slot switches 200, 201. Theoperation of the time-division bus is described more closely inconnection with FIG. 5.

FIG. 3 is a flowchart of the external operation of the time slot switchaccording to the invention (FIG. 2). In step 301, the time slot switchis synchronized with PCM data from the Abis interface (FIG. 2, 103).Thereafter, the necessary time slot configuration data are received 302at the local operations and maintenance unit (FIG. 2, 106) O&M.Subsequently, these configuration data, i.e. information on from whichtime slot of the Abis interface the data to a certain transceiver unitTRX is to be picked or into which time slot of the Abis interface it isto be inserted, are sent 303 to the time slot switch, more specifically,to its time slot selection registers (FIG. 2, 205, 212). Thereafter,after, the operation of the time slot switch is divided into twobranches 305 and 306. If branch 305 is chosen, the time slot switch(FIG. 2, 200) receives data from the Abis interface (FIG. 2, 103) instep 307 and sends the data to the transceiver unit TRX (FIG. 2, 108) instep 309. If branch 306 is chosen, the time slot switch (FIG. 2, 200)receives data 308 from the transceiver unit TRX (FIG. 2, 108) and sends(310) this data to the correct time slot on the Abis interface (FIG. 2,103). Both branches 305, 306 of operation are then combined, and thetime slot switch determines 312 whether it should change theconfiguration data. If the configuration data must be changed, i.e. ifthe data to or from the transceiver unit TRX is to be transmitted to orreceived from a different time slot on the Abis interface, the time slotswitch loads again new configuration data into the local operations andmaintenance unit or some other operations and maintenance unit,whereafter the implementation of the invention is continued inaccordance with the flowchart shown in the figure. The reason for theconfiguration change will be explained in the following. Thetransceivers 107, 108 test their operation all the time by various testsand test loops. Examples of these tests are memory tests for theinternal units of transceivers, tests for asic circuits, and testing ofinterfaces between connections and operations of units. In addition,there are time slot tests, testing of incoming clock signals, andtesting or frame numbers. There is also temperature testing oftransceiver units to control that the temperature of the unit is keptwithin suitable limits. Other possible tests are testing of frequenciesthat are used and testing of power levels. The results of all of thesetests are conducted to the local operations and maintenance unit O&M106. This is performed in such a manner that the transceiver units sendinformation on their state regularly or at suitable intervals to thelocal O&M unit, for instance over the 2-Mbit/s serial bus 220. Theoperations and maintenance unit checks that none of the test resultscalls for measures. If,however, one of the tests gives an alarm, i.e.such a fault has occurred that the transceiver unit concerned must beswitched off, the operations and maintenance centre switches thetransceiver off. The switching off is effected in such a manner that theenable signal 221, 222 supplied to the buffers 207, 217 of the time slotswitch 200 in the transceiver unit 108 is cut off, whereby the buffersenter into three-condition and no longer transmit the informationforward. At the same time, the O&M unit switches off the power supply ofthe transceiver unit 108. The redundant transceiver is then brought intouse in such a manner that the O&M unit starts the power supply of theunit to be brought into use, i.e. switches on its power supply, and thevalues corresponding with those time slots from which the time slotswitch will take information from the time-division bus or into which itwill insert information are fed into those time slot registers of thetime slot switch which are assigned to the transceiver unit concerned.If the O&M unit observes that the error message given does not requirethat the operating transceiver unit be changed to another one, the O&Munit does not effect a configuration change, and the following step isto determine 315 whether the time slot switch is to be reset. If theanswer is positive 316, the operation returns to step 301, from which itcontinues in accordance with the diagram. If the answer is negative 317,the operation continues as previously: the old configuration data 303are set to the time slot switch, whereafter the operation continues asdescribed above. It should be noted that the local operations andmaintenance unit 106 can be in contact with other network elementsthrough the bus 223. Thus, the local O&M unit can be controlled by acentralized operations and maintenance centre, the base stationcontroller or the switching centre of the radio system.

FIG. 4 is a flowchart of the internal operation of the time slot switchof the invention (FIG. 2, 200). At first that time slot of thetransceiver on the time-division bus (202) from which data are to bepicked to the radio path or, correspondingly, the identifier of thattime slot on the internal bus of the base station in which data are tobe transmitted from the base station to the Abis interface (FIG. 2, 103)is written to the time slot selection register (FIG. 2, 205, 212).Thereafter, the time slot counter (FIG. 2, 204 or 214) must beincremented, whereafter the comparing means (FIG. 2, 206, 215) start toperform comparative operations 404 in which the state of the time slotselection register is compared with that of the time slot counter. Ifthe states are not identical 405, the time slot counter is incremented402 again and the comparative operation is attempted once more; if thestate of the time slot selection register is identical 406 with that ofthe time slot counter, the operation continues in such a manner that thedata contained in the time slot is transmitted in the downlink directionfrom the buffer (FIG. 2, 207) to the transceiver TRX (FIG. 2).Correspondingly, in the uplink direction, the data taken from a certaintime slot of the transceiver and stored in the buffer (FIG. 2, 217) istransmitted to the internal bus (FIG. 2, 202) of the base station andfrom there to the multiplexer/demultiplexer means to be furthertransferred to the Abis interface (FIG. 2, 103). After this datatransmission, the operation of the time slot switch returns to step 402,in which the time slot counters are incremented, whereafter theoperation continues as described above.

FIG. 5 is a timing diagram of the internal data transmission bus at thebase station of the cellular radio system. The base station compriseseither several time slot switches or one time slot switch which isprovided with the necessary time slot registers, counters, comparingmeans and buffers per each transceiver unit of the base station. Thetime slot switches that are provided for each transceiver unit or thecorresponding parts are connected to the multiplexer/demultiplexer means(FIG. 2, 104) through the internal time-division 2-Mbit/s bus. The busis timed by the use of a synchronization signal SYNC and a clock signalCLOCK obtained from the same bus. Both of the signals are generated inthe multiplexer/demultiplexer means (FIG. 2, 104) using either theinternal clock of the multiplexer or an extremely accurate PCM clocksignal obtained through the Abis interface. In FIG. 5, time isrepresented running from the right to the left. In the internaltime-division bus of the base station, the length of one frame is 125μs, and one frame consists of 32 time slots, which are numbered 0 . . .31 in the figure. Each time slot contains 8 bits. A frame contains thus32*8=256 bits, and the recurrence frequency of the frame is 8000 timesper second. The operation of the bus is described in the following. Thetime slot counters (FIG. 2, 204, 214) of the time slot switches count atthe rising edge of the clock signal CLOCK, and a sample of incoming datais always taken at the falling edge. In the downlink direction, i.e. inthe transmission of data from the base station controller and theswitching centre to a subscriber station, or mobile phone, the time slotswitch picks the bits contained in the time slots assigned to thetransceiver connected to the time slot switch, i.e. the data from theinternal 2-Mbit/s bus of the base station, by means of time slot gridsand time slot counter logic. Correspondingly, in the uplink direction,i.e. in the transmission of data from a subscriber station to the basestation controller and the switching centre, the time slots aretransmitted to the internal bus of the base station in the time slotsassigned to the transceiver unit concerned. The transceiver unit iselectrically connected to the internal bus of the base station by meansof three-condition buffers, which guide the data to the bus when theyreceive time slots assigned to them and are in a high-impedance statewhen they receive other time slots.

The drawings and the descriptions relating thereto are intended merelyto illustrate the inventive concept. In its details the base station fora cellular radio system and the cellular radio system according to theinvention may vary within the scope of the appended claims. Although theinvention has been described above mainly in connection with the GSMmobile phone system, it may also be used in other cellular radionetworks.

I claim:
 1. A base station for a cellular radio system which has aplurality of switching centres and plurality of base stations connectedthereto by respective base station controllers through time-divisionrespective telecommunication links, and an operations and maintenancecentre, the base station comprising:a plurality of transceiver units, atime-division bus providing respective time slots for the base station,a multiplexer/demultiplexer means for multiplexing saidtelecommunication links and for demultiplexing data to be sent from saidtime-division bus of said base station to said telecommunication links,at least one switching means for selectively switching respective of thetransceiver units to respective of the telecommunication links, theswitching means being a time slot switch comprising:a time slot counterfor synchronizing the time slot switch with the time slots of thetime-division bus, a time slot selection register responsive tooperations and maintenance information including time slot selectiondata for time slot-specific storing and reading of said time slotselection data, a comparing means for comparing the time slot selectiondata contained in the time slot selection register with the state of thetime slot counter at a given point of time in such a manner that thetime slot selection data is compared with the state of the time slotcounter and, responsive to the result of this comparison, the datecontained in a respective time slot on a respective of saidtelecommunication links or at a respective one of the transceiver unitsis transmitted forward, a buffer means responsive to the data suppliedby the comparing means for storing data contained on the respective oneof said telecommunication links and for feeding the data into arespective one of the transceiver units, and for feeding data containedat a respective one of said transceiver units into the desired time sloton the respective one of said telecommunication links.
 2. The basestation of claim 1, wherein:said switching means of said base station isarranged to be controlled by an operations and maintenance unit of saidcellular radio system in such a manner that the transmission capacity ofsaid telecommunication links is allocated for the traffic between thoseof said base stations and said base station controllers or those of saidswitching centres of said cellular radio system and the base stationswhich need additional transmission capacity.
 3. The base station ofclaim 2, wherein:there is one the switching means per each saidtransceiver unit of said base station.
 4. The base station of claim 2,wherein:the switching means said base station is arranged to beresponsive to base station-specific operation and to maintenance units,which are provided and control operation of said base station.
 5. Thebase station of claim 2, wherein:said switching means of said basestation is arranged to be responsive to a respective base stationcontroller of said cellular radio system, which controls operation ofsaid base station, to the respective switching centre of said cellularradio system, or to said operations and maintenance centre of saidcellular radio system.
 6. The base station of claim 2, wherein:wheninformation is transmitted from a respective said switching centre ofsaid cellular radio system to a respective the transceiver unit of saidbase station, said time slot switch is arranged for picking the datafrom a time slot assigned to the transceiver unit on the time-divisionbus.
 7. The base station of claim 2, wherein:when information istransmitted from a respective said transceiver unit of said base stationin said cellular radio system to a respective said switching centre ofsaid the cellular radio system, said time slot switch is arranged fortransmitting the data to said time-division bus in a time slot assignedto the respective the transceiver unit to be further transmitted overthe respective said telecommunication link to the respective theswitching centre of said cellular radio system or to the respective thebase station controller.
 8. The base station of claim 2, wherein:saidswitching means is arranged to be controlled in such a manner that whenone of said transceiver units of said base station becomes broken, anoperative one of the transceiver units is allocated in place of saidbroken transceiver unit, the operative transceiver unit is assigned therespective time slot of the respective telecommunication link which saidbroken transceiver unit had until then been assigned.
 9. The basestation of claim 1, wherein:there is one the switching means per eachsaid transceiver unit of said base station.
 10. The base station ofclaim 1, wherein:the switching means of said base station is arranged tobe responsive to base station-specific operation and to maintenanceunits, which are provided and control operation of said base station.11. The base station of claim 1, wherein:the switching means of saidbase station is arranged to be responsive to a respective base stationcontroller of said cellular radio system, which controls operation ofsaid base station, to the respective switching centre of said cellularradio system, or to said operations and maintenance centre of saidcellular radio system.
 12. The base station of claim 1, wherein:wheninformation is transmitted from a respective the switching centre ofsaid the cellular radio system to a respective the transceiver unit ofsaid base station, said the time slot switch is arranged for picking thedata from a time slot assigned to the transceiver unit on thetime-division bus.
 13. The base station of claim 1, wherein:wheninformation is transmitted from a respective said transceiver unit ofsaid base station in said cellular radio system to a respective saidswitching centre of said cellular radio system, said time slot switch isarranged for transmitting the data to said time-division bus in a timeslot assigned to the respective the transceiver unit to be furthertransmitted over the respective said telecommunication link to therespective the switching centre of said cellular radio system or to therespective the base station controller.
 14. The base station of claim 1,wherein:said switching means is arranged to be controlled in such amanner that when one of said transceiver units of said base stationbecomes broken, an operative one of the transceiver units is allocatedin place of said broken transceiver unit, the operative transceiver unitis assigned the respective time slot of the respective telecommunicationlink which said broken transceiver unit had until then been assigned.